The invention relates to a method and apparatus for sharpening the knives of a chipper. Specifically applicable are chippers that produce shreds and chips for subsequent industrial processing, such as raw material for particle board. A significant problem with such chippers is the relatively short service life of the knives. Due to wear, they need to be replaced after only a few hours of operation, that is, several times per shift.
The installation of new, sharp knives involves particular expense. The desired chip thickness depends on the knife overhang beyond the so-called wear plates, which, in turn, are an integral part of the knife rim. It follows that the replacement of dull knives by sharp ones is time-consuming and costly. Labor costs are especially high.
As a result, means have been long-sought to economize the knife replacement. Known from German patent DE 43 16 514 C2 is a method comprising the following steps: First, the knife basket is removed from the chipper and placed in a basket carrier, in which it is mounted rotatably and envelopes a grinding system with a grinding wheel. The dull knives in the basket are first released from their clamping holder, whereupon the knife overhang is adjusted to that needed to allow grinding the knives to a desired working overhang. Next, a slow, continuous rotation is imparted to the knife basket. The grinding system advances simultaneously in the axial direction of the knife basket, and thus along the cutting edges of the knives.
Owing to the continuous and thus uninterrupted rotation of the referenced prior art knife basket, the resulting knife end faces are disposed on a circular arc. It is thus impossible to grind a so-called relief angle. Regarding the relief angle, the referenced patent states that grinding in a built-in state, of necessity, produces a relief angle of zero. Many experts, however, are of the opinion that a relief angle may be desirable.